From all that I read and know, medical records are not accessible by employers, police or insurance companies. These last especially not as our medical insurance is not run for profit by private companies.
I've never read about it being any great concern here.
In the UK the Police can obtain Medical Record access where there is a sufficient ‘Public Interest’ argument that the Public's interest overrides the individuals' right to confidentiality:
https://www.bma.org.uk/advice-and-support/ethics/medical-students/ethics-toolkit-for-medical-students/when-police-request-access-to-patient-records
Regarding Insurance, anyone claiming on a medical policy would have to sign over access to their records, to verify no pre-existing conditions, or else forfeit their claim. It's in the standard policy T&C. They don't make checks on your health when you take your Travel Insurance policy out, but require access if you claim for getting sick abroad etc.
In the UK there's even a statutory duty on Healthcare Professionals to report extremist views that may be expressed by patients they treat:
https://www.gov.uk/government/publications/prevent-duty-guidance/revised-prevent-duty-guidance-for-england-and-wales
Retired Doctors answering the recent call for medical volunteers to help with the mass Covid vaccination, were turned away if they had not had this ‘Prevent Counter-Terrorism’ training, despite the ‘patients’ being a random selection of strangers seen for 5 mins max.
No one should consider what they say to their Doctor to be completely confidential.